The long-term objectives of this project are an understanding of the impact of conductive hearing losses on binaural hearing, an understanding of the effects of middle ear surgery on binaural hearing, and a means of predicting whether middle ear surgery can be used to restore binaural hearing in a given conductively impaired patient. It is often taken for granted that middle ear surgery will improve binaural hearing: the present project will test this assumption directly. The specific aims of the present investigation are to assess the effects of stapedectomy and tympanoplasty on binaural hearing, examining the factors of 1) the symmetry of the hearing loss, 2) the severity of the hearing loss, 3) the etiology of the hearing loss, 4) the effect of a cochlear component of the hearing loss (as measured by frequency selectivity and by bone conduction threshold), and 5) the specific kind of cue underlying performance (interaural time vs interaural amplitude disparity). All stimuli will be presented over earphones in order to control precisely the type of cue available. The binaural tests will include lateralization by the cue of interaural time difference, and detection in noise (Masking Level Difference) by the cues of either interaural time difference or interaural amplitude difference. A monaural test of frequency selectivity (notched noise method) will be used as a measure of cochlear function. Testing will be performed in a sound-treated room, and a three interval, three alternative, forced-choice adaptive procedure will be used in all tasks. Subjects will include a normal-hearing control group (n=12), patients having otosclerosis with symmetrical hearing (n=12), patients having otosclerosis with asymmetrical hearing (n=12), patients otitis media with symmetrical hearing (n=12), and patients having otitis media with asymmetrical hearing (n=12). Testing will be performed before and four months after middle ear surgery. Data will be analyzed using analysis of variance and correlation procedures.